How Mikania micrantha (Lahare banmara) destroy the forest and agricultural crops in residential area of Nepal?

What is Mikania micrantha ?

Mikania micrantha is a perennial creeping climber known for its vigorous and rampant growth. It is branchy, slender-stemmed perennial vine. The leaves are arranged in opposite pairs along the stems and are heart-shaped or triangular with an acute tip and a broad base. Leaves may be 4-13cm long. The flowers, each 3-5mm long, are arranged in dense terminal or axillary corymbs. Individual florets are white to greenish-white. The seed is black, linear-oblong, five-angled and about 2mm long. Each seed has a terminal pappus of white bristles that facilitates dispersal by wind or on the hair of animals.

Occurrence place and distribution

Mikania micrantha grows best where fertility, organic matter, soil moisture and humidity are all high. It damages or kills other plants by cutting out the light and smothering them. It is a native of central and South America where it grows in and near forests, along rivers, streams and roadsides. Mikania micrantha was introduced into India after the Second World War to camouflage airfields and is one of the most widespread and problematic weeds in the Pacific region. It occurs in agricultural areas, coastland, natural forests, planted forests, riparian zones, disturbed, scrub/shrub lands, urban areas, wetlands. It has been reported as a weed in India, Bangladesh, Sri Lanka, Mauritius, Thailand, the Philippines, Malaysia, Indonesia, Papua New Guinea and many of the Pacific islands. It was first identified in Queensland, Australia in 1998, but had been present there for between 8 - 10 years already. This species has been nominated as among 100 of the "World's Worst" invaders.

Impacts on agricultural crop and tree

Once established, Mikania micrantha spreads at an alarming rate, readily climbing and twining on any vertical support, including crops, bushes, trees, walls and fences. Its shoots have been reported to grow up to 27mm a day. Vegetative reproduction is also efficient and vigorous. Although intolerant of heavy shade it readily colonises gaps. Mikania micrantha damages or kills other plants by cutting out the light and smothering them. In this respect it is especially damaging in young plantations and nurseries. It also competes for water and nutrients, but perhaps even more importantly, it is believed that the plant releases substances that inhibit the growth of other plants (IUCN/SSC,2005).

Mikania micrantha climbing on the temporary wall and fence of a household in Saptary

Appearance in residential area of Nepal

Mikania micrantha first appears in eastern part of Nepal. Few years ago it is seen in the Koshi Tappu and Chitwan national park but it spread in near by area, forest and rural area. Villagers of Sunsary and Saptary used to collect thatch grasses which was affected by and source of mikania seeds from Koshi Tappu. Now it got spread in rural area and impacts on agricultural crop mainly climber type of vegetables. Marginal land where there is less tillage and disturbance are suitable place for its growth. As it grows fast dominate other climber type of vegetables and kill slowly. Farmers are fade up of its negative impact on agricultural crops. Farmers are unknown to its nature of regeneration so that they are not able to control or eradicate.

How it is spreading in the forest?

It is spreading in the Tarai from east to west and first seen around Koshi tappu and Chitwan national park area where climatic condition is favorable for survival. On the way of Narayanghat to Mugling it is seen on roadside both in community forest and national forest. In area where plenty of moisture available, it grows rapidly. In most of the cases young Sal regeneration and seedlings are being damaged. Open ground is fully covered by Mikania, in that place regeneration is impossible in normal condition because even seeds of Sal disperse from near by area do not contact with soil due to thick ground cover. Once it invades the area won't provide favorable condition for light demander species to regenerate. In bigger tree its effect is less in terms of growth but certainly effects on regeneration. It appears where there is canopy open and moist soil. At present it is seen in the forest near Gaidakot and Rajhar area. Till now it is not seen is Rupandehi and Kapilvastu. But it will easily spread up to Sal zone.

Trunk of Sal tree and ground covered by Mikania in Chautari CF, Nawalparasi

Reproduction and Local dispersal methods

It reproduces sexually by seeds and vegetatively by rooting at nodes. A single plant may cover over 25 square meters within a few months, and release as many as 40,000 viable seeds every year. In some locations flowering and seed production are during short days only.

On animals: seeds are dispersed in clothing or hair, when people and animal travelling during fruiting period. Seeds are also dispersed by wind so that it is spreading easily and rapidly from both means.

Management or eradication of Mikania

As it is spreading very fast in suitable area mostly forest and marginal land, it is necessary to control or eradicate from invading forest land. There are several methods to manage or control of Mikania such as:

Chemical: Control of Mikania micrantha is difficult because of the high output of viable seeds, and because new plants can grow from even the tiniest stem fragments. Other than complete destruction of all the stems, herbicides provide the only suitable method of control at present. But that is not viable and applicable in Nepal because of cost and technology.

Biological: Liothrips mikaniae appears to be specific and to have considerable potential as a biological control organism. A number of other natural enemies of little known specificity also attacks Mikania micrantha (Waterhouse and Norris, 1987). Fungal pathogens have also been investigated in India as a potential biological control method (Swarbrick, 1997 in PIER, 2003).

In our case both chemical and biological methods are not feasible. It is suggested that it would be better to uproot or destroy when it is seen in small area. Uprooting before flowering and burning would be the best option to control from wider spreading.

Conclusion

Mikania micrantha is plant killing weeds and which is mostly affects young regeneration and creates unfavorable condition for regeneration. It is newly seen in Nepal and it is not in people's notice. Several countries and territories are trying to manage the major weeds of the region but result seen is not effective. It can be reduced or eradicated through creating shade which is not suitable for Mikania micrantha. Several community forests are also affected by this weeds which can be eradicated through user participation. It is important to control or destroy in very beginning before dispersal of seeds. If it is spread widely will reduce the productivity, destroy regeneration and degrade the forest condition. Once it proliferated throughout the forest then will become costly to control by any means. Control burning is also one way to contain chances of wider spreading.